Currently, swaged collar fasteners are frequently utilized to fasten workpieces, which usually consist of two or more plates or panels having substantially aligned openings. The fastener includes a collar and a pin. The pin has a head on one end, and a pintail with lock-grooves and pull-grooves on the opposite the end. The pin is inserted through the aligned openings from one side of the workpiece, and a collar is inserted over the pin at the opposite side of the workpiece for subsequent swaging to the pin. When set or installed, the pin head engages the outside surface of one of the plate members and the collar engages the outside surface of the other plate member.
One conventional method for setting the collar on the pin is by the use of a pull-type installation tool which grasps and pulls the pull-grooves of the pin while simultaneously applying a reaction force to the collar. After a certain pulling force is reached, the collar is locked on the pin by the depression of the collar metal flowing into the lock-grooves on the pin. More particularly, the installation tool includes a jaw assembly, which engages the pull-grooves on the pintail, and a swaging anvil, which engages the collar. As the tool is actuated, the jaws exert a pulling action on the pin and the swaging anvil applies the reaction force to the collar. As the work-piece plates are drawn together, the pin head engages the outside surface of one of the plates and the collar engages the outside surface of the other plate. Continued pulling action of the tool increases the tool swaging load as the swaging anvil strokes or progresses over the collar in the direction of the flange of the collar. When the installation tool breaks off the pull-groove portion of the pintail from the pin, at the completion of the swaging action, the installation tool is removed and the installation of the collar fastener is complete.
With a collar design having a constant shank wall thickness, during the swaging process, part of the collar material is gradually forward extruded, thereby increasing the installation tool swaging load necessary to fully swage the collar. More particularly, as the anvil of the installation tool progresses over the collar shank material, the material is deformed against the pin by the anvil. During this process, part of the shank material that is adjacent to the contact point of the anvil is also pushed forward to form a forward-extrusion. The forward-extrusion is the portion of the shank material that is pushed ahead of the anvil. In other words, the thickness of the shank wall increases ahead of the tool, as the tool displaces material forward. The increase in thickness in the shank wall produces increases in tool swaging loads that are undesirable.
What is also needed is a built-in mechanism to stop the progression of the anvil of the installation tool, when it reaches an adequate depth or stroke length on the collar. For instance, the installation tool might displace the anvil all the way to the flange of the collar or the sheet line zone (i.e., the zone on the surface of the workpiece that mates with the bottom of the flange). This creates high peak pressure on the collar bearing surface that bears on the sheet line zone, which promotes collar splaying (i.e., curling of portions of the flange away from the sheet line zone of the workpiece). High peak pressure also poses the risk of damage to work-piece members that are made of sensitive materials such as composites.